基于文献计量的全球海洋酸化研究状况分析

海洋酸化(Ocean acidification)为目前备受人们关注的全球性问题。因此为了能够客观地揭示海洋酸化的研究态势,研究采用文献计量分析(Bibliometric analysis)的方法,以海洋酸化概念提出后(2004年以后)ISI Web of Science期刊引文数据库中涉及到海洋酸化研究的所有文献为样本,对文献的增长趋势及期刊分布进行描述统计,并基于关键词的知识图谱及突变分析的方法探究海洋酸化的热点关注方向随时间的变动及研究前沿。描述统计表明:海洋酸化概念提出的这十多年来,涉及海洋酸化的研究文献数量呈现激增的态势,研究学科交叉明显,海洋酸化对珊瑚礁的影响是这十年来的重点研究领域。从基于关键词的知识图谱可以看到,在海洋酸化研究初期(2004—2009年),研究内容主要分为两个部分,一是海洋酸化对海洋生物(尤其是珊瑚礁生物及浮游植物)及生态系统的影响;二是对海洋酸化现象的认识;中期(2010—2015年),研究内容与初期相似,研究重点往海洋生物上倾斜,同时有新的热点研究区域和研究方向的出现;近期(2016年以后),海洋酸化对海洋生物影响的研究依旧占据着主流研究方向。对基于突变分析得到的当前(2018年2月)海洋酸化研究的热点关注的文献分析发现,当前海洋酸化的研究存在以下5个前沿方向:(1)在探究海洋酸化与生物的关系之时需结合多因子讨论;(2)探索生物在海洋酸化下的内在应对机制;(3)海洋酸化影响下的生物响应的综合评估及预测;(4)探索海洋酸化对海洋生态系统的影响;(5)对海洋酸化概念的挑战——海洋酸化形成原因的探索。     

A chloroquine-resistant Swiss 3T3 cell line with a defect in late endocytic acidification

To investigate the role of acidification in cell proliferation, several cell lines resistant to chloroquine were isolated with the expectation that some would express altered endocytic acidification. The preliminary characterization of one of these lines, CHL60-64, is described. In contrast to endocytic mutants described previously, the initial phase of endocytic acidification, as measured by transferrin acidification, is normal in this cell line. However, a difference in subsequent endocytic acidification was observed in CHL60-64. In the parental cells, internalized dextran was fully acidified to approximately pH 5.5 within 1 h. In CHL60-64, the pH in the endocytic compartment was only 6.1 after 1 h and remained as high as 5.8 for at least 4 h. After an 8-h incubation, the pH decreased to 5.5, indicating that the second phase of acidification is only slowed in CHL60-64, and not blocked. Consistent with this retarded acidification, ATP-dependent acidification in vitro (as measured by acridine orange accumulation) was reduced in both the lysosomal fraction and the endosomal fraction isolated from CHL60-64. A decrease in the in vivo rate of acridine orange accumulation after perturbation with amine was also observed. In addition to amine resistance and defective acidification, CHL60-64 was found to be resistant to vacuolation in the presence of chloroquine and ammonium chloride, and was resistant to ouabain. Further studies on this new class of endocytosis mutant, in combination with existing mutants, should help to clarify the mechanisms responsible for the regulation of endocytic acidification.     

Research on acidification in forest soil driven by atmospheric nitrogen deposition

Soil acidification is defined as the process in which exchangeable cations are leaching and soil H⁺ concentration is raising thereby increases soil acidity. Changes in soil pH value and acid neutralizing capacity are mainly indicators of soil acidification. Soil acidification is considered to be a serious ecological and environmental issue, which not only reduces soil quality, but also decreases biodiversity of forest ecosystem and induces forest decline. With nitrogen (N) deposition rapidly increasing, its contribution to soil acidification becomes a major concern in the world. However, the impact of increased N deposition on soil acidification is not well addressed highlighting the need for further attention to the issue. In this paper, the studies on forest soil acidification induced by N deposition were reviewed. The factors related to soil acidification driven by N deposition were classified and discussed, which included soil acidic buffering capacity, N components in atmospheric N deposition, climate, plant species in forests, and N status in ecosystem. Iron (Fe) buffering phase and the consequent Fe toxicity occurring to the acidified soil caused by high N deposition were concerned. The scarcity of phosphorus (P) element induced by soil acidification was particularly emphasized. The research methods used to study soil acidification driven by N deposition were also evaluated. In the end we stressed the importance of the study on soil acidification especially in tropical and subtropical regions driven by N deposition and its mechanisms. This paper can serve for maintaining sustainable forest and agricultural ecosystems.     

Measurements of the acidification kinetics of single SynaptopHluorin vesicles

Uptake of neurotransmitters into synaptic vesicles is driven by the proton gradient established across the vesicle membrane. The acidification of synaptic vesicles, therefore, is a crucial component of vesicle function. Here we present measurements of acidification rate constants from isolated, single synaptic vesicles. Vesicles were purified from mice expressing a fusion protein termed SynaptopHluorin created by the fusion of VAMP/synaptobrevin to the pH-sensitive super-ecliptic green fluorescent protein. We calibrated SynaptopHluorin fluorescence to determine the relationship between fluorescence intensity and internal vesicle pH, and used these values to measure the rate constant of vesicle acidification. We also measured the effects of ATP, glutamate, and chloride on acidification. We report acidification time constants of 500 ms to 1 s. The rate of acidification increased with increasing extravesicular concentrations of ATP and glutamate. These data provide an upper and a lower bound for vesicle acidification and indicate that vesicle readiness can be regulated by changes in energy and transmitter availability.     

Mitochondria are not required for death receptor-mediated cytosolic acidification during apoptosis

In addition to cell shrinkage, membrane blebbing, DNA fragmentation and phosphatidylserine exposure, intracellular acidification represents a hallmark of apoptosis. Although the mechanisms underlying cytosolic acidification during apoptosis remained largely elusive, a pivotal role of mitochondria has been proposed. In order to investigate the involvement of mitochondria in cytosolic acidification during apoptosis, we blocked the mitochondrial death pathway by overexpression of Bcl-2 and subsequently activated the death receptor pathway by anti-CD95 or TRAIL or the mitochondrial pathway by staurosporine. We show that Bcl-2 but not caspase inhibition prevented staurosporine-induced intracellular acidification. Thus, intracellular acidification in mitochondrial apoptosis is a Bcl-2-inhibitable, but caspase-independent process. In contrast, Bcl-2 only slightly delayed, but did not prevent intracellular acidification upon triggering of death receptors. The Na⁺/H⁺ exchanger NHE1 was partially degraded during apoptosis but only to a small extent and and at a delayed time point when cytosolic acidification was almost completed. We therefore conclude that cytosolic acidification is mitochondrially controlled in response to mitochondria-dependent death stimuli, but requires additional caspase-dependent mechanisms during death receptor-mediated apoptosis. Michaela Waibel, Stefan Kramer and Kirsten Lauber share equal first authorship.     

Phagosomal acidification is mediated by a vacuolar-type H(+)-ATPase in murine macrophages

The mechanism underlying phagosomal acidification was studied in thioglycolate-elicited murine macrophages. The pH of the phagosomal compartment (pHp) was measured fluorimetrically in macrophage suspensions following ingestion of fluorescein isothiocyanate-labeled Staphylococcus aureus. At 37 degrees C, pHp decreased rapidly, reaching a steady state value of 5.8-6.1, while the cytoplasmic pH remained near neutrality, pH 7.1. The phagosome to cytosol pH gradient could be collapsed by addition of nigericin, monensin, or weak bases. The substrate dependence and inhibitor sensitivity profile of phagosomal acidification were investigated in intact and permeabilized cells. Phagosomal acidification was inhibited when ATP was depleted using metabolic inhibitors or permeabilizing the plasma membrane by electroporation. In permeabilized cells, acidification could be initiated by readdition of both Mg2+ and ATP. Neither adenosine 5'-(beta,gamma-imido)triphosphate nor adenosine 5'-(gamma-thio)triphosphate supported phagosomal acidification. Inhibitors of F1F0-type H(+)-ATPase such as oligomycin and azide, and the E1E2-type H(+)-ATPase inhibitor vanadate had no effect on phagosomal acidification. In contrast, the rate of phagosomal acidification was reduced by micromolar concentrations of N-ethylmaleimide and N,N'-dicyclohexylcarbodiimide. In permeabilized cells, nitrate inhibited the acidification with an apparent Ki of 25 mM. Phagosomal acidification was also effectively blocked by the macrolide antibiotic bafilomycin A1, with an apparent Ki of approximately 3 mM in both intact and electroporated cells. In this concentration range, bafilomycin A1 selectively inhibits vacuolar H(+)-ATPases. The substrate requirement and inhibitor susceptibility profile of phagosomal acidification strongly suggest that proton translocation across the phagosomal membrane is mediated by a vacuolar-type H(+)-ATPase.     

海洋酸化对蟹类影响的研究进展

人类活动排放二氧化碳引起了海水碳酸盐平衡体系变化和pH下降, 最终导致了“海洋酸化”。海洋酸化对蟹类产生了从表观到分子的多重影响。文章在总结海洋酸化对各种蟹类生长发育、生理与代谢、表型和行为等方面影响的基础上, 对其影响的机理展开了讨论, 并对控制海洋酸化及其对蟹类的影响研究提出了意见和建议。     

Acidification and alkalinization of lakes by experimental addition of nitrogen compounds

Fertilization of a small lake with ammonium chloride for four years as part of a eutrophication experiment caused it to acidify to pH values as low as 4.6. Implications for acidification of lakes via precipitation polluted with ammonium compounds are discussed.When phosphate was supplied with the ammonium, biological nitrogen uptake, apparently by phytoplankton, was the main mechanism causing acidification. When ammonium was applied without phosphate, it accumulated to high concentrations in solution, after which nitrification caused rapid acidification. In both cases, the whole-lake efficiency of acidification was low, averaging about 13% of the potential acidification of supplied ammonium chloride (Table 2).Subsequent application of phosphate plus sodium nitrate for two years caused the pH of the lake to increase. The efficiency of alkalinization was higher than for acidification, averaging 69% of the potential alkalinization of the supplied sodium nitrate.     

The mechanism of intracellular acidification induced by glucose in Saccharomyces cerevisiae

Addition of glucose or fructose to cells of Saccharomyces cerevisiae adapted to grow in the absence of glucose induced an acidification of the intracellular medium. This acidification appeared to be due to the phosphorylation of the sugar since: (i) glucose analogues which are not efficiently phosphorylated did not induce internal acidification; (ii) glucose addition did not cause internal acidification in a mutant deficient in all the three sugar-phosphorylating enzymes; (iii) fructose did not affect the intracellular pH in a double mutant having only glucokinase activity; (iv) glucose was as effective as fructose in inducing the internal pH drop in a mutant deficient in phosphoglucose isomerase activity; and (v) in strains deficient in two of the three sugar-phosphorylating activities, there was a good correlation between the specific glucose- or fructose-phosphorylating activity of cell extracts and the sugar-induced internal acidification. In addition, in whole cells any of the three yeast sugar kinases were capable of mediating the internal acidification described. Glucose-induced internal acidification was observed even when yeast cells were suspended in growth medium and in cells suspended in buffer containing K+, which supports the possible signalling function of the glucose-induced internal acidification. Evaluation of internal pH by following fluorescence changes of fluorescein-loaded cells indicated that the change in intracellular pH occurred immediately after addition of sugar. The apparent Km for glucose in this process was 2 mM. Changes in both the internal and external pH were determined and it was found that the internal acidification induced by glucose was followed by a partial alkalinization coincident with the initiation of H+ efflux. This reversal of acidification could be due to the activity of the H+-ATPase, since it was inhibited by diethylstilboestrol. Coincidence between internal alkalinization and the H+ efflux was also observed after addition of ethanol.     

Characteristics of Fe‐deficiency‐induced acidification in subterranean clover

Iron-deficiency-induced acidification is one of the important reactions of plant Fe-deficiency-stress response, but the overall understanding of this reaction is limited. The characteristics of Fe-deficiency-induced acidification of subterranean clover (subclover) (Trifolium brachycalycinum Katzn. and Morley cv. Koala) were studied in this paper. Plants were grown hydroponically under -Fe conditions, and Fe-deficiency-induced acidification was determined using pH-stat, back-titration and chemical equilibrium procedures. Fe-deficiency-induced acidification was undetectable during the first day after Fe-deficiency stress initiation, but the maximum acidification rate was attained by the second day, when plants exhibited visual chlorosis symptoms. The acidification rate was relatively constant with increasing Fe-deficiency chlorosis, suggesting that a critical level of Fe deficiency was needed to trigger acidification, but that once the acidification process was initiated, the intensity of acidification was independent of severity of Fe deficiency. Net H⁺-release (PR) rate determined using a chemical equilibrium method and net acidity release (AR) rate determined using a back-titration method were practically identical, indicating that Fe-deficiency-induced acidification involved almost entirely the release of free H⁺, not organic acid. In the assay temperature range of 5 to 35°C, PR rate was highest at about 20°C. Net acidity release rate was almost totally inhibited at pH values ≤4.5 and increased with increasing assay pH up to pH 9. The pH effect occurred within 30 min of incubation initiation, implying that the effect of pH is probably on the activity of H⁺ transport through the plasma membrane, not on the quantity of responsible protein(s). Cations were required in the incubation solution for Fe-deficiency-induced acidification. Divalent cations in the assay solution resulted in a higher AR rate than monovalent cations, and essential cations resulted in a higher AR rate than non-essential cations, indicating that the relative effectiveness of cations is related to the efficiency of their absorption by plant roots. These results are discussed in relation to their practical significance and the mechanisms of Fe-deficiency-induced acidification.     

Mechanism of cadmium-induced cytotoxicity in rat hepatocytes

Exposure of rat hepatocytes to cadmium below 50 μM for a short period (10 min) resulted in cellular acidification. Conversely, exposure to Cd more than 50 μM for a long period (60 min) caused cellular alkalinization accompanied by membrane damage as reflected by decrease in cellular K content and loss of intracellular lactic dehydrogenase. In hepatocytes exposed to 5 μM Cd, a concentration sufficient to induce acidification without cytotoxicity, the metal was preferentially associated with the crude nuclei and cell debris fractions, suggesting an interaction between Cd and cell membranes to cause acidification. Omission of bicarbonate from the incubation medium induced cellular acidification. The presence of Cd in this medium did not potentiate the medium-induced acidification. Mg-ATP (25 μM) induced cellular acidification in relation to an increase in the concentration of cytosolic free Ca. The coexistence of Mg-ATP and Cd at the concentrations which had no effect on cellular pH in the presence of either agants induced cellular acidification. These observations suggest that Cd induced cellular acidification by modulating the process connected with the rise in cytosolic free Ca via interaction with plasma membranes. This acidification had no strong immediate cytotoxic actions but led to subsequent cellular alkalinization accompanied with severe cytotoxicity and membrane breakage.     

Effects of fishing and acidification‐related benthic mortality on the southeast Australian marine ecosystem

Oceanic uptake of anthropogenic carbon dioxide (CO₂) is altering the carbonate chemistry of seawater, with potentially negative consequences for many calcifying marine organisms. At the same time, increasing fisheries exploitation is impacting on marine ecosystems. Here, using increased benthic‐invertebrate mortality as a proxy for effects of ocean acidification, the potential impact of the two stressors of fishing and acidification on the southeast Australian marine ecosystem to year 2050 was explored. The individual and interaction effects of the two stressors on biomass and diversity were examined for the entire ecosystem and for regional assemblages. For 61 functional groups or species, the cumulative effects of moderate ocean acidification and fishing were additive (30%), synergistic (33%), and antagonistic (37%). Strong ocean acidification resulted in additive (22%), synergistic (40%), and antagonistic (38%) effects. The greatest impact was on the demersal food web, with fishing impacting predation and acidification affecting benthic production. Areas that have been subject to intensive fishing were the most susceptible to acidification effect, although fishing also mitigated some of the decline in biodiversity observed with moderate acidification. The model suggested that ocean acidification and long‐term fisheries exploitation could act synergistically with the increasing sensitivity to change from long‐term (decades) fisheries exploitation potentially causing unexpected restructuring of the pelagic and demersal food webs. Major regime shifts occur around year 2040. Greater focus is needed on how differential fisheries exploitation of marine resources may exacerbate or accelerate effects of environmental changes such as ocean acidification.     

Nitrite Transport in Chloroplast Inner Envelope Vesicles (I. Direct Measurement of Proton-Linked Transport)

Chloroplast inner envelope membrane vesicles that are loaded with the pH-sensitive fluorophore, pyranine, show rapid internal acidification when nitrite is added. Acidification is dependent upon [delta]pH, with the inside of vesicles being alkaline with respect to the outside. The rate of vesicle acidification was directly proportional to the concentration of nitrite that was added and the imposed pH difference across the membrane. In contrast, added nitrate had no effect on vesicle acidification. Nitrite also caused acidification of asolectin vesicles. The extent of vesicle acidification is dependent on the internal volume of vesicles. Inner envelope and asolectin vesicles that were prepared by extrusion were approximately the same size, allowing them to be compared when the final extent of acidification, measured after the pH gradient had collapsed, was similar. The rate of nitrite-dependent acidification was similar in these two preparations at any single nitrite concentration. These results indicate that nitrite movement occurs by rapid diffusion across membranes as nitrous acid, and this movement is dependent on a proton gradient across the lipid bilayer. Under conditions approximating those in vivo, the rate of diffusion of nitrous acid far exceeds that of nitrite reduction within chloroplasts.     

Coastal acidification impacts on shell mineral structure of bivalve mollusks

Ocean acidification is occurring globally through increasing CO₂ absorption into the oceans creating particular concern for calcifying species. In addition to ocean acidification, near shore marine habitats are exposed to the deleterious effects of runoff from acid sulfate soils which also decreases environmental pH. This coastal acidification is being exacerbated by climate change‐driven sea‐level rise and catchment‐driven flooding. In response to reduction in habitat pH by ocean and coastal acidification, mollusks are predicted to produce thinner shells of lower structural integrity and reduced mechanical properties threatening mollusk aquaculture. Here, we present the first study to examine oyster biomineralization under acid sulfate soil acidification in a region where growth of commercial bivalve species has declined in recent decades. Examination of the crystallography of the shells of the Sydney rock oyster, Saccostrea glomerata, by electron back scatter diffraction analyses revealed that the signal of environmental acidification is evident in the structure of the biomineral. Saccostrea glomerata, shows phenotypic plasticity, as evident in the disruption of crystallographic control over biomineralization in populations living in coastal acidification sites. Our results indicate that reduced sizes of these oysters for commercial sale may be due to the limited capacity of oysters to biomineralize under acidification conditions. As the impact of this catchment source acidification will continue to be exacerbated by climate change with likely effects on coastal aquaculture in many places across the globe, management strategies will be required to maintain the sustainable culture of these key resources.     

磷元素和土壤酸化交互作用对核桃幼苗光合特性的影响

核桃(Juglans regia)向南推广种植不可避免地会遇到土壤酸化和缺磷的环境, 这种环境如何影响核桃的生长是生产中需要知晓的基础问题。该文研究了土壤不同pH值对核桃的磷素营养影响以及缺磷对核桃幼苗水分平衡、光合特性和生长的影响。在温室内采用砂培盆栽试验, 研究一年生核桃嫁接幼苗在不同pH值、磷水平基质中的水分关系、光合特性和生长的应对机制。研究设4种处理, 即: 对照(正常供应磷素+ pH 6.0); 正常供应磷素+ pH 3.0; 不添加磷素+ pH 6.0; 不添加磷素+ pH 3.0。结果显示: pH值与磷素对核桃幼苗的影响是两个相互独立的过程, 酸性(pH值3.0)条件下, 核桃幼苗根系生物量降低、根冠比减小, 根系导水率降低, 对磷素的吸收利用减少, 尽管其供磷正常, 但各生长指标及生理指标与磷胁迫条件下反应相似; 两因素具有一定的叠加性, 在磷胁迫条件下, 酸化(pH值3.0)对核桃幼苗的损害进一步加剧。各指标具体变化如下: 酸化及磷胁迫条件下核桃根系水分导度降低, 叶柄木质部结构改变, 导管密度降低, 木质部导管栓塞程度增加, 叶柄导水率下降, 植株水分运输效率降低, 叶片水势降低, 诱导气孔关闭; 气孔导度降低, 光合作用能力下降; 胁迫条件下, 叶绿素荧光参数最大光化学效率低于0.8, 实际光化学效率、光化学淬灭下降, 非光化学淬灭增加, 核桃幼苗受胁迫环境损害, 叶片光系统II光合电子传递活性受到抑制, 光合能力下降。总之, 土壤酸化抑制了核桃幼苗对磷元素的吸收利用, 造成体内缺磷; 磷胁迫及酸化抑制了叶柄木质部的发育, 降低了根系水分导度和叶柄导水率, 干扰了核桃幼苗水分平衡, 通过气孔与非气孔共同调节, 限制了核桃幼苗光合作用, 抑制了核桃幼苗高生长、直径生长及叶面积增加; 但并没有发现土壤酸化和缺磷之间有明显的交互作用。     

海洋酸化对珊瑚礁生态系统的影响研究进展

目前,大气CO2浓度的升高已导致海水pH值比工业革命前下降了约0.1,海水碳酸盐平衡体系随之变化,进而影响珊瑚礁生态系统的健康。近年来的研究表明海洋酸化导致造礁石珊瑚幼体补充和群落恢复更加困难,造礁石珊瑚和其它造礁生物(Reef-building organisms)钙化率降低甚至溶解,乃至影响珊瑚礁鱼类的生命活动。虽然海洋酸化对造礁石珊瑚光合作用的影响不显著,但珊瑚-虫黄藻共生体系会受到一定影响。建议选择典型海区进行长期系统监测,结合室内与原位模拟试验,从个体、种群、群落到系统不同层面,运用生理学和分子生物学技术,结合生态学研究手段,综合研究珊瑚的相应响应,以期深入认识海洋酸化对珊瑚礁生态系统健康(例如珊瑚白化)的影响及其效应。     

Calcium Requirement for Indoleacetic Acid-induced Acidification by Avena Coleoptiles

The ionic specificity of IAA-induced acidification by Avena coleoptiles was studied, using zwitterionic, presumably impermeant buffers. The acidification was almost totally dependent on divalent cations with an order of effectiveness of Ca(2+) >/= Sr(2+) > Mn(2+), Mg(2+); whereas other polyvalent cations tested were ineffective. The Ca(2+) response was IAA-dependent. The CaCl(2) concentration was optimal at 0.3 to 1 mm and inhibitory at higher concentrations. Sr(2+) inhibited Ca(2+)-dependent acidification and monovalent cations such as K(+) did not induce additional acidification in the presence of optimal CaCl(2). These data are consistent with a mechanism for IAA-induced acidification involving a Ca(2+) -H(+) exchange.     

Selectively bred oysters can alter their biomineralization pathways,promoting resilience to environmental acidification

Commercial shellfish aquaculture is vulnerable to the impacts of ocean acidification driven by increasing carbon dioxide (CO₂) absorption by the ocean as well as to coastal acidification driven by land run off and rising sea level. These drivers of environmental acidification have deleterious effects on biomineralization. We investigated shell biomineralization of selectively bred and wild‐type families of the Sydney rock oyster Saccostrea glomerata in a study of oysters being farmed in estuaries at aquaculture leases differing in environmental acidification. The contrasting estuarine pH regimes enabled us to determine the mechanisms of shell growth and the vulnerability of this species to contemporary environmental acidification. Determination of the source of carbon, the mechanism of carbon uptake and use of carbon in biomineral formation are key to understanding the vulnerability of shellfish aquaculture to contemporary and future environmental acidification. We, therefore, characterized the crystallography and carbon uptake in the shells of S. glomerata, resident in habitats subjected to coastal acidification, using high‐resolution electron backscatter diffraction and carbon isotope analyses (as δ¹³C). We show that oyster families selectively bred for fast growth and families selected for disease resistance can alter their mechanisms of calcite crystal biomineralization, promoting resilience to acidification. The responses of S. glomerata to acidification in their estuarine habitat provide key insights into mechanisms of mollusc shell growth under future climate change conditions. Importantly, we show that selective breeding in oysters is likely to be an important global mitigation strategy for sustainable shellfish aquaculture to withstand future climate‐driven change to habitat acidification.     

Ocean acidification impairs crab foraging behaviour

Anthropogenic elevation of atmospheric CO₂ is driving global-scale ocean acidification, which consequently influences calcification rates of many marine invertebrates and potentially alters their susceptibility to predation. Ocean acidification may also impair an organism''s ability to process environmental and biological cues. These counteracting impacts make it challenging to predict how acidification will alter species interactions and community structure. To examine effects of acidification on consumptive and behavioural interactions between mud crabs (Panopeus herbstii) and oysters (Crassostrea virginica), oysters were reared with and without caged crabs for 71 days at three pCO₂ levels. During subsequent predation trials, acidification reduced prey consumption, handling time and duration of unsuccessful predation attempt. These negative effects of ocean acidification on crab foraging behaviour more than offset any benefit to crabs resulting from a reduction in the net rate of oyster calcification. These findings reveal that efforts to evaluate how acidification will alter marine food webs should include quantifying impacts on both calcification rates and animal behaviour.     

Acidification reduces mitochondrial calcium uptake in rat cardiac mitochondria

Cardiac ischemia-reperfusion (I/R) injury is accompanied by intracellular acidification that can lead to cytosolic and mitochondrial calcium overload. However, the effect of cytosolic acidification on mitochondrial pH (pHm) and mitochondrial Ca2+ (Cam2+) handling is not well understood. In the present study, we tested the hypothesis that changes in pHm during cytosolic acidification can modulate Cam2+ handling in cardiac mitochondria. pHm was measured in permeabilized rat ventricular myocytes with the use of confocal microscopy and the pH-sensitive fluorescent probe carboxyseminaphthorhodafluor-1. The contributions of the mitochondrial Na+/H+ exchanger (NHEm) and the K+/H+ exchanger (KHEm) to pHm regulation were evaluated using acidification and recovery protocols to mimic the changes in pH observed during I/R. Cam2+ transport in isolated mitochondria was measured using spectrophotometry and fluorimetry, and the mitochondrial membrane potential was measured using a tetraphenylphosphonium electrode. Cytosolic acidification (pH 6.8) resulted in acidification of mitochondria. The degree of mitochondrial acidification and recovery was found to be largely dependent on the activity of the KHEm. However, the NHEm was observed to contribute to the recovery of pHm following acidification in K+-free solutions as well as the maintenance of pHm during respiratory inhibition. Acidification resulted in mitochondrial depolarization and a decrease in the rate of net Cam2+ uptake, whereas restoration of pH following acidification increased Cam2+ uptake. These findings are consistent with an important role for cytosolic acidification in determining pHm and Cam2+ handling in cardiac mitochondria under conditions of Ca2+ overload. Consequently, interventions that alter pHm can limit Cam2+ overload and injury during I/R.